Method of assembling an electromechanical device in a gas-turbine engine

ABSTRACT

A method of assembling an electromechanical device in a gas-turbine engine, including mounting a rotor of the device on a rotor support, securing a stator of the device to a stator support, coupling the rotor support to the stator support such that said rotor is rotatable about said stator, securing the device to a bearing support, securing a bearing assembly on the low pressure shaft, coupling the device to the low pressure shaft by installing the bearing support over the bearing assembly, and drivingly engaging the rotor support to the high pressure shaft.

TECHNICAL FIELD

The application relates generally to gas turbine engines and, moreparticularly, to electromechanical devices in such an engine.

BACKGROUND OF THE ART

A known method of installing an internal starter/generator in a gasturbine engine includes attaching the rotating component of the internalstarter/generator cantilevered from the forward end of the high pressureshaft of the engine. This usually results in additional rotating weighton the high pressure shaft and as such may have an adverse effect on thedynamics of the high pressure shaft. As such, the addition of aninternal starter/generator to an engine not originally designed toaccept one may necessitate a redesign of the high pressure shaft tosupport the additional loads associated with the starter/generator,displacement of bearing supports to accommodate the starter/generatorwhich may require a redesign of the low pressure shaft, and/or changesin the low pressure shaft support structure requiring retesting theengine for blade-off and bird-ingestion, any of which may result insubstantial development costs.

SUMMARY

In one aspect, there is provided a method of assembling anelectromechanical device in a gas-turbine engine having independentlyrotatable and concentric low pressure and high pressure shafts, the lowpressure shaft having a portion extending beyond the high pressure shaftsupported by at least one bearing assembly, the method comprising:mounting a rotor of the device on a rotor support; securing a stator ofthe device to a stator support; coupling the rotor support to the statorsupport such that said rotor is rotatable about said stator; securingthe device to a bearing support; securing a selected one of the at leastone bearing assembly on the low pressure shaft; coupling the device tothe low pressure shaft by installing the bearing support over theselected bearing assembly; and drivingly engaging the rotor support tothe high pressure shaft.

In another aspect, there is provided a method of assembling astarter/generator in a gas-turbine engine, the method comprising:coupling a rotor and a stator of the starter/generator such that therotor is rotatable with respect to the stator to drive the rotor whenthe starter/generator is electrically powered and to produce electricalpower when the rotor is rotated; securing the stator to a bearingsupport; coupling the starter/generator device to a low pressure shaftof the engine by installing the bearing support over a bearing assemblysecured to an end of the low pressure shaft; inserting the low pressureshaft through a high pressure shaft of the engine with the end of thelow pressure shaft protruding therefrom and positioning thestarter/generator in proximity of an end of the high pressure shaft; anddrivingly engaging the rotor to the high pressure shaft.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine;

FIG. 2 is a schematic cross-sectional side view illustrating a portionof a gas-turbine engine and an internal electromechanical device inaccordance with a particular embodiment;

FIG. 3 is a schematic cross-sectional view illustrating a portion of agas-turbine engine and an internal electromechanical device inaccordance with another particular embodiment;

FIG. 4 is a schematic cross-sectional view illustrating a portion of agas-turbine engine and a step in the assembly of an internalelectromechanical device therein, in accordance with a particularembodiment; and

FIG. 5 is a schematic sectional side view showing a low pressure shaftassembly, illustrating another step in the assembly of the startergenerator in accordance with a particular embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a gas turbine engine 10 of a type preferably providedfor use in subsonic flight, generally comprising in serial flowcommunication a fan 12 through which ambient air is propelled, acompressor section 14 for pressurizing the air, a combustor 16 in whichthe compressed air is mixed with fuel and ignited for generating anannular stream of hot combustion gases, and a turbine section 18 forextracting energy from the combustion gases. A high pressure shaft 19drivingly interconnects high pressure rotors of the compressor andturbine sections 14, 18. A low pressure shaft 20 rotatable independentlyfrom the high pressure shaft 19 drivingly interconnects the fan 12 andlow pressure rotor(s) of the turbine section 18. Although not shown, thelow pressure shaft 20 may also support additional low pressure rotor(s)of the compressor section 14. The low pressure shaft 20 is hollow andextends through the high pressure shaft 19 beyond each end thereof.Although the engine 10 is illustrated as a turbofan engine, alternatelythe engine may be any other adequate type of gas turbine engine, such asfor example a turboprop or a turboshaft engine.

Referring to FIG. 2, the portion of the low pressure shaft 20 protrudingfrom the high pressure shaft 19 is supported by first and second spacedapart bearing assemblies 42, 50 each received in a respective beatingcavity 33, 29, the first bearing assembly 42 being located closer to theend of the low pressure shaft 20, and as such further from the highpressure shaft 19, than the second bearing assembly 50. Anelectromechanical device 21 is described herein and is installed betweenthe two spaced apart bearing assemblies 50, 42 about the low pressureshaft 20 to be driven by the high pressure shaft 19. In a particularembodiment, the electromechanical device is a starter/generator. Theelectromechanical device 21 is an internal device as it is receivedradially inwardly with respect to the flowpath of the engine. In aparticular embodiment, the internal electromechanical device 21 isreceived within one or more bearing housings.

Referring to FIG. 2, there is shown the manner in which the device 21 issupported about the low pressure shaft 20. As herein shown, the device21 is provided with a stator 22 and a rotational rotor 23 which isrotatable about the stator 22. The stator 22 is housed in a stationarystator support 24 which is secured to a bearing support 25′ of thesecond bearing assembly 50. The rotor 23 is secured to an arm of a rotorsupport 25. A ring gear 25″ is secured to an arm of the rotor support25. The device gear 25″ has a series of circumferential teeth 32. A ringgear 26 is further secured about the end of the high pressure shaft 19and rotated therewith. The shaft gear 26 has a series of bevelled gearteeth 27 thereabout.

In order to transfer the drive between the shaft gear 26 and the devicegear 25″ to produce electricity by the device 21 when in a generatormode and/or to use the device 21 to drive the high pressure shaft 19when in a starter mode, these gears have to be coupled. In theembodiment shown, this is achieved by mounting a coupling idle gear 28in the bearing cavity 29 associated with the second bearing assembly 50.The coupling idle gear 28 has circumferential teeth gear 31 which are intoothed engagement with the bevel gear teeth 27 of the shaft gear 26 andthe bevel gear teeth 32 of the device gear 25″. As herein shown, thecoupling idle gear 28 has a hub 40 which is configured for rotationaldisplacement in a support assembly 30 secured to stationary componentsof bearing support 25′. When the high pressure shaft 19 is rotated, itwill cause rotation of the coupling idle gear 28 which in turn rotatesthe device gear 25″ thereby displacing the rotor support 25 and therotor 23 about the stator 22 of the device to produce electricity.Additionally or alternately, when the rotor 23 is rotated as the device21 is powered, the device gear 25″ rotates the idle gear 28 which inturn rotates the high pressure shaft 19 through the shaft gear 26. It ispointed out that the rotating components of the device 21 are fullysupported independent of other rotating engine components by the samestructure as the bearing support 25′ associated with the second bearingassembly 50. In a particular embodiment, replacement of an externalstarter/generator driven by a power shaft by the device 21 driven by theintermediate coupling idle gear 28 supported in the bearing cavity 29allows for the bearing support 25′ to remain at the same location sothat the shaft dynamics of the low pressure shaft 20 may be maintained,and so that the dynamics of the high pressure shaft 19 may be unaffectedby the device installation.

In summary, the method of operating the device 21 generally comprisesthe steps of mounting the electromechanical device 21 about the lowpressure shaft 20 of a gas turbine engine with the rotor 23 of thedevice 21 mounted on the rotor support 25, having the device gear 25″secured thereto, and supported about the low pressure shaft 20 by thebearing support 25′. The method further comprises securing the shaftgear 26 about the high pressure shaft 19. Still further, the methodcomprises coupling the shaft gear 26 to the device gear 25″ through thecoupling idle gear 28 rotationally supported by a stationary gearsupport immovably mounted in the bearing cavity 29.

It can be appreciated that the ratio between the number of the bevelledgear teeth of the shaft gear 26, the coupling idle gear 28 and thedevice gear 25″ determines the rotational speed of the rotor 23 inrelation to the high pressure shaft speed. Accordingly, the rotor drivespeed can be stepped up or down.

Referring to FIG. 3, there is shown a further embodiment of a gearcoupling ratio between the high pressure shaft 19 and the device gear25″, allowing for a step-up speed relationship. As herein shown, a shaftring gear 35 has a conical section 45 rearwardly projecting in thebearing cavity 29. Circumferential teeth 46 are disposed about thelarger outer periphery of the conical section 45 and are in toothedengagement with the teeth 31′ of a smaller coupling idle gear 28′. Theteeth 31′ of the coupling idle gear 28′ are also in toothed engagementwith the teeth 32 of the device gear 25″. Accordingly, it can be seenthat by modifying the size of the shaft gears 26, 35 and the couplingidle gear 28, 28′ that the relative rotational speed of the rotor 23with respect to that of the high pressure shaft 19 can be modified.

Referring now to FIGS. 4 and 5, there will be described the method ofassembling the device 21 in a gas turbine engine and about the lowpressure shaft 20 thereof and between bearing assemblies 42, 50.

The method comprises mounting the rotational rotor 23 of the device 21on the rotor support 25 which is provided with the device gear 25″. Thebearings 47 of the rotor support 25 are installed on a support sleeve 48of the rotor support 25. The stator 22 of the device 21 is secured tothe stator support 24. The rotor support 25 of the rotor 23 is coupledto a stator housing 49 to rotate about the stator housing with thestator 22 immovably supported therein. The stator support 24 is thensecured to the bearing support 25′ of the second bearing assembly 50.The second bearing assembly 50 is then secured, herein by press-fittingit on the low pressure shaft 20. The stator support 24 and the rotorsupport 25 of the rotor 23 coupled for rotation thereabout are theninstalled over the bearing assembly 50 to form a low pressure shaftassembly as shown in FIG. 5.

As shown in FIG. 4, the bearing support 25′ is provided with an annularflange 51 which is fitted over the second bearing assembly 50 and thebearings 47 supported on the support sleeve 48 of the rotor support 25are retained in position by a ledge on the surface of the flange 51.This secures the bearings and the support sleeve 48 captive butrotatable on its bearing support. Accordingly, the internal statorgenerator with its connection to the bearing support 25′ is now mountedon the low pressure shaft 20, as shown in FIG. 5.

As shown in FIG. 4, the bearing support 25′ is also provided with aconnecting portion 52 having a flange 52′ which is immovably connectedto a flange 54′ of the bearing housing 54 by a series of bolts 53thereabout. The bearing housing 55 of the first bearing assembly 42 isalso provided with a flange 55′ which is interconnectable with theflanges 52′ and 54′ of the second bearing housing 54 and the connectingportion 52 for connection therewith. This is done by different boltsafter the flanges 52′ and 54′ are interconnected.

Before the first bearing housing 55 is secured over the device 21, thepower cable 56 are routed from inside the second bearing housing 54through the bearing support 25′ and over the stator support 24. Thepower cable 56 is then secured to cable connectors 57 mounted exteriorlyon the front end of the stator support 24. The device gear 25″ may becoupled to the coupling idle gear 28 during the mounting of the bearingsupport 25′ over the bearings or thereafter. The method therefore alsodriveably engaging the high pressure shaft 19 and the rotor 23 of thedevice 21 and in the particular embodiment shown this includes bysecuring the shaft gear 26 to the high pressure shaft 19, rotationallyinstalling the idle gear 28 on a support in the second bearing cavity 29or attached to a gear support 60 securable or integrally formed on theouter face of the bearing support 25′ of the second bearing assembly 50,and meshing the idle gear 28 with the shaft gear 26 and the device gear25″, as shown in FIG. 3.

In a particular embodiment the idle gear 28 is engaged with the devicegear 25″ and assembled with the low pressure shaft assembly (includingthe device 21 and the bearing support 25′). The shaft gear 26 isassembled to the high pressure shaft 19 before the installation of thelow pressure shaft assembly to the second bearing housing 54. Assemblyof the low pressure shaft assembly to the second bearing housing 54engages the teeth of the idle gear 28 and of the shaft gear 26.

In an alternate embodiment, the idle gear 28, 28′ may be replaced by anyother adequate type of member allowing a driving engagement, includingbut not limited to a lay shaft.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.For example, by modifying the gear ratios, a desired rotor drive speedcan be obtained and modified. Still other modifications which fallwithin the scope of the present invention will be apparent to thoseskilled in the art, in light of a review of this disclosure, and suchmodifications are intended to fall within the appended claims.

1. A method of assembling an electromechanical device in a gas-turbineengine having independently rotatable and concentric low pressure andhigh pressure shafts, the low pressure shaft having a portion extendingbeyond the high pressure shaft supported by at least one bearingassembly, the method comprising: mounting a rotor of the device on arotor support; securing a stator of the device to a stator support;coupling the rotor support to the stator support such that said rotor isrotatable about said stator; securing the device to a bearing support;securing a selected one of the at least one bearing assembly on the lowpressure shaft; coupling the device to the low pressure shaft byinstalling the bearing support over the selected bearing assembly; anddrivingly engaging the rotor support to the high pressure shaft.
 2. Themethod as defined in claim 1, wherein the rotor support includes adevice gear, and drivingly engaging the rotor support to the highpressure shaft includes meshing an idle gear with the device gear andwith a gear extending from the high pressure shaft.
 3. The method asdefined in claim 2, wherein the idle gear is rotationally secured to thebearing support and received in a bearing housing of the selectedbearing assembly.
 4. The method as defined in claim 1, wherein couplingthe rotor support to the stator support includes installing bearings ona support sleeve portion of the rotor support and coupling the rotorsupport to the stator support through the bearings.
 5. The method asdefined in claim 1, wherein the at least one bearing assembly includesfirst and second bearing assemblies with the second bearing assemblybeing located closer to the high pressure shaft than the first bearingassembly when the low pressure shaft and high pressure shaft areassembled in the engine, and wherein the device is secured to thebearing support of the second bearing assembly, the second bearingassembly is secured on the low pressure shaft, and the device is coupledto the low pressure shaft by installing the bearing support over thesecond bearing assembly.
 6. The method as defined in claim 5, furthercomprising enclosing the device in a housing of the first bearingassembly to secure the device and the low pressure shaft to the engine.7. The method as defined in claim 6, wherein enclosing the device in thehousing of the first bearing assembly includes immovably securing thehousing of the first bearing assembly to the bearing support and to ahousing of the second bearing assembly.
 8. The method as defined inclaim 1, wherein after coupling the device to the low pressure shaft,power cables of the device are routed over the stator support andsecured to cable connectors secured to the stator support.
 9. The methodas defined in claim 1, wherein installing the bearing support over theselected bearing assembly includes positioning an annular flange of thebearing support about the selected bearing assembly with bearings on thesupport portion of the rotor support retained captive for rotation aboutthe annular flange, and immovably securing a connecting portion of thebearing support to a housing of the selected bearing assembly.
 10. Themethod as defined in claim 1, wherein the selected bearing assembly ispress-fitted on the low pressure shaft.
 11. The method as defined inclaim 1, wherein the low pressure shaft is engaged in the high pressureshaft after the device is coupled to the low pressure shaft.
 12. Amethod of assembling a starter/generator in a gas-turbine engine, themethod comprising: coupling a rotor and a stator of thestarter/generator such that the rotor is rotatable with respect to thestator to drive the rotor when the starter/generator is electricallypowered and to produce electrical power when the rotor is rotated;securing the stator to a bearing support; coupling the starter/generatorto a low pressure shaft of the engine by installing the bearing supportover a bearing assembly secured to an end of the low pressure shaft;inserting the low pressure shaft through a high pressure shaft of theengine with the end of the low pressure shaft protruding therefrom andpositioning the starter/generator in proximity of an end of the highpressure shaft; and drivingly engaging the rotor to the high pressureshaft.
 13. The method as defined in claim 12, wherein drivingly engagingthe rotor to the high pressure shaft includes meshing an idle gear witha gear extending from a rotor support connected to the rotor and with agear extending from the high pressure shaft.
 14. The method as definedin claim 13, wherein the idle gear is rotationally secured to thebearing support and received in a bearing housing of the bearingassembly.
 15. The method as defined in claim 12, wherein coupling therotor to the stator includes installing bearings on a support sleeveportion of a rotor support connected to the rotor and coupling the rotorsupport to a stator support connected to the stator through thebearings.
 16. The method as defined in claim 12, wherein the end of thelow pressure shaft is supported by an additional bearing assembly spacedapart from the end of the high pressure shaft, and the starter/generatoris coupled to the low pressure shaft such as to be located between theadditional bearing assembly and the end of the high pressure shaft. 17.The method as defined in claim 16, further comprising enclosing thestarter/generator in a housing of the additional bearing assembly tosecure the starter/generator and the low pressure shaft to the engine.18. The method as defined in claim 17, wherein enclosing thestarter/generator in the housing of the additional bearing assemblyincludes immovably securing the housing of the additional bearingassembly to the bearing support and to a housing of the bearingassembly.
 19. The method as defined in claim 12, wherein after couplingthe starter/generator to the low pressure shaft, power cables are routedover the a support of the stator and secured to cable connectors securedto the support.
 20. The method as defined in claim 12, whereininstalling the bearing support over the bearing assembly includespositioning an annular flange of the bearing support about the bearingassembly with bearings on a support of the rotor retained captive forrotation about the annular flange, and immovably securing a connectingportion of the bearing support to a housing of the bearing assembly. 21.A method of assembling a starter/generator in a gas-turbine enginehaving independently rotatable and concentric low pressure and highpressure shafts, the method comprising: mounting a rotor of thestarter/generator on a rotor support; securing a stator of thestarter/generator to a stator support; coupling the rotor support to thestator support such that said rotor is rotatable about said stator todrive the rotor when the starter/generator is electrically powered andto produce electrical power when the rotor is rotated; securing thestator support to a bearing support; securing a bearing assembly on anend portion of the low pressure shaft; coupling the starter/generator tothe low pressure shaft by installing the bearing support over theselected bearing assembly; inserting the low pressure shaft through thehigh pressure shaft with the end of the low pressure shaft protrudingtherefrom and positioning the starter/generator in proximity of an endof the high pressure shaft; and drivingly engaging the rotor support tothe high pressure shaft.